The basic principle of operation for magnetic tape drive systems, cartridge or non-cartridge, that utilize thin, flexible, endless peripheral belts to transfer the tape from one reel pack to another under tension, is the two pulley, flat belt drive. In such a belt drive, one pulley is "the driver" and the other is the "driven" pulley or load. The endless belt contacts each of the reel packs to urge the packs to rotate in the desired manner to transfer the strip media i.e. tape, under tension, between the reel packs past, for example, a read/write head.
In such a system there exists a slack (low tension) and a taut (high tension) side of the endless belt, the taut side always being downstream of the driven pulley in the direction of motion of the belt and between the driver and driven pulley. Since any elastic material stretches under tension, the taut side of the endless belt is thinner than the slack side and since such belt drives are always endless closed loop systems, continuity of mass flow must exist by the laws of physics. This means that at any point in the belt drive, an equal amount of belt mass must pass per unit time. Thus, the velocity of the belt on the taut side of a belt drive must be greater than the velocity of the belt on the slack side by an amount proportionate to the difference in thickness. It follows that with the taut side of the belt engaging the take-up reel pack and the slack side contacting the supply reel pack that the take-up pack is urged to rotate at a greater tangential velocity than the supply reel pack. This, in turn, tensions the tape being transferred between the reel packs.
Magnetic tape cartridges have been produced in varying configurations and in a wide range of capabilities for applications in audio, analog and digital recording. One type of tape cartridge which provides for tension of the strip media is disclosed in U.S. Pat. No. 4,242,709 issued Dec. 30, 1980 to Stricker. This cartridge relies upon rolling friction between engaging rollers to tension the traveling belt trapped therebetween, the belt driving the cartridge reel packs.